Urban Health Issues

Defining Urban Areas

One of the key challenges that faces epidemiologic inquiry about health in cities and how city characteristics influence health is that there is little consensus about the definition of urban and what constitutes a city. The U.S. Bureau of the Census defines an urbanized area by specifying a minimum population (50,000 people) and a particular minimum population density (1,000 people per square mile). The Census Bureau thus provides a dichotomy whereby territory, population, and housing units within specific size and density parameters are designated as urban and those that are outside those parameters are nonurban. However, there are inherent limitations to these definitions; urban areas exist in contrast to rural or simply in contrast to nonurban areas. In the 21st century, only a few cities, such as Las Vegas, exist in extreme isolation where what is not defined as city is rural. Most cities (e.g., New York City, London, Bangkok) are actually far-reaching densely populated areas, containing periurban and suburban areas, which continue relatively uninterrupted for miles beyond the municipal city boundaries and the city center. To accommodate varying conceptions of what constitutes an urban area, alternative definitions have been developed. They vary in how they define rates of disease, risk, and protective behaviors.

The definition of urban also varies widely between countries. Among 228 countries for which the United Nations had data in 2000, almost half (100) include size and density as criteria, 96 include administrative definitions of urban (e.g., living in the capital city), 33 include functional characteristics (e.g., economic activity, available services), 24 have no definition of urban, and 12 define all (e.g., Anguilla, Bermuda, the Cayman Islands, Gibraltar, the Holy See, Hong Kong, Monaco, Nauru, Singapore) or none (e.g., Pitcairn Island, Tokelau, and Wallis and Futuna Islands) of their population as urban. Official statistics (e.g., United Nations statistics detailed above) rely on country-specific designations and, as such, vary widely. In specific instances, definitions of urban in adjacent countries vary tremendously (e.g., Cambodia vs. Vietnam). Furthermore, definitions of urban have evolved in different ways in different countries. Therefore, global statistics are subject to country-level differences in the definition of urban that may be based on population density or specific urban features (e.g., proportion of agricultural workers, municipal services).

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